The present invention relates to a method for provisioning of subscribed Quality of Service or QoS guarantees for multimedia services to a user in a framework of telecommunication networks when this user communicates from a network different from his home network. It also relates to a telecommunication network for a framework of networks in which common rules are followed, such as, for instance, the Universal Mobile Telecommunication System UMTS. It also relates to user equipment that communicates with a Proxy Call State Control Function P-CSCF in the network from which it is either calling or called, by means of extensions of Session Initiation Protocol SIP/Session Description Protocol SDP messages for the handling of multimedia components in accordance with Quality of Service QoS requirements for a call corresponding to a multimedia communication session.
As known, multimedia systems offer services with much more Quality of Service QoS variants than the classical circuit switched networks. Therefore, it is one of the major objectives of multimedia telecommunication systems, such as UMTS Release 5, to provide services corresponding to different needs with appropriate resource allocations. Accordingly, the user expects and requests a proper end-to-end Quality of Service for every service for which he has a subscription with his home network even when such a service has to be provided by other networks associated with his home network in a telecommunication framework. Taking UMTS as an example of the telecommunication framework, the “home network” is the network with which the user made his initial service subscription, the “visited network” is the network to which the roaming user is currently attached. It is clear that when the user is not roaming outside its home network, in that case the visited network is equal to the user's home network.
Right now, network operators can define service policies for their respective networks. These service policies, defining the rules by which the operator will allow users access to his services, are detailed in the user's service profile, which is negotiated between the home operator and the users, via subscription. Each operator enforces his own service policies on his own network, via his own service policy control mechanisms. Network operators can also define resource policies for their respective networks. Resource policies define the rules that a network operator uses to authorize requests to use his transport/bearer resources. Each operator enforces his own resource policies on his own network, via his own resource policy control mechanisms. Policy control mechanisms, such as Common Open Policy Service protocol COPS of the Internet Engineering Task Force IETF, provide means to network operators for enforcing local policies in their respective networks from a Policy Decision Point PDP onto a Policy Enforcement Point PEP.
As known, Next Generation Networks NGN, are packet based networks employing new multimedia call control, management and signaling protocols, e.g., SIP/SDP or H.323, to provide from narrow-band voice telephony services to broadband multimedia services to users and particularly with users requesting qualities of service and particularly transmission bandwidths well adapted to their needs.
3GPP has decided to use a Session Initiation Protocol/Session Description Protocol SIP/SDP suite as the single call control protocol suite for the UMTS R5 multimedia domain. In the SIP/SDP protocol suite, SIP messages are used for multimedia call control signaling between end parties, i.e., the calling or called party user equipment or terminal, and intermediate SIP call control nodes, which are called CSCF in UMTS. SDP offers the possibility to attach additional information fields to a SIP message containing a more detailed description about the session's multimedia components. This invention relates to extensions to the SIP/SDP suite used for transmitting user perceived Quality of Service QoS characteristics. It has to be remarked that, this invention only discusses, but is not limited to, QoS extensions to SIP/SDP. H.323 is another protocol suite used for multimedia call control in the fixed world. Consequently, although only QoS extensions to SIP/SDP are described as a preferred example in this invention, similar QoS extensions could equally be applied to other present, such as H.323, or even future multimedia protocol suites.
Although this invention uses as preferred example the UMTS SIP/SDP multimedia architecture, which is based on SIP call control elements called Call State Control Functions CSCF, it could equally apply to other multimedia call control architectures, e.g., the H.323 architecture whose call control elements are called H.323 Gate Keepers.
Similarly GPRS, the bearer system for 3GPP UMTS networks, is only used as a preferred example in this invention. The invention equally applies to other bearer networks, such as Asymmetric Digital Subscriber Line ADSL used in NGN networks.
In Next Generation Networks NGN, there is a split between bearer control and call control, meaning that call control signaling can follow a totally different route than the bearer path. In UMTS, as an example of such a NGN network, bearer control comprises Generic Packet Radio System GPRS elements, such as Serving GPRS Support Node SGSN and Gateway GPRS Support Node GGSN, and call control comprises Session Initiation Protocol SIP call control elements, more specifically Proxy Call State Control Function P-CSCF and Serving Call state Control Function S-CSCF. In UMTS, the bearer path goes via SGSN and GGSN, both located in the visited network, directly towards its destination. The call control path goes from the P-CSCF, located in the visited network, first via the S-CSCF in the home network, before going towards its destination.
In UMTS service policy control is enforced by the home network from a PDP, coupled to the Service Platform SP or Home Subscriber Server HSS, onto a PEP, coupled to the Serving Call State Control Function S-CSCF. Resource policy control is enforced by the visited network from a PDP, coupled to the Proxy Call State Control Function P-CSCF, onto a PEP, coupled to the Gateway GPRS Support Node GGSN. As the SIP/SDP call control always pass through a S-CSCF in the home network, whereas the bearer path always goes directly from the GGSN in the visited network to its destination, it is clear that therefore, service policy control which is under control of home network, and resource policy control which is under control of visited network, are completely uncorrelated. Accordingly, if there is a local network failure or overload situation in the visited network, there is no possibility of having any service information from the home network taken into account in the visited network for a visiting user, when a downgrading of quality of service is enforced for users visiting this visited network. So currently there is no way for home operators to give their customers guarantees that a high Quality of Service, according to the subscription paid for by the user, can be maintained when the user communicates by means of a visited network, even if such a maintaining would be desirable in the present situation.